There has been employed many kinds of lifting apparatus capable of raising operators and materials to an elevated location for assembling, painting, repairing a building and the like or repairing and inspecting an indoor ceiling, or maintaining illumination equipment and the like.
There has also been recently employed a lifting apparatus capable of raising the platform on which the operators and materials are loaded to an elevated location far beyond the operator's reach. In working at a position which is far beyond the operator's reach, ladders or scaffolds are conventionally employed. If ladders are used, the height which can be reached is limited and it is laborious to raise the materials. If scaffolds are assembled at the working site, it takes much time for assembling and removing the scaffolds which results in low efficiency.
To meet the demand, there has been employed several lifting apparatus capable of stretching vertically and having wheels capable of moving on the floor. In such a lifting apparatus, a plurality of masts are assembled so as to be stretchable vertically by hydraulic apparatus or winches so that a platform fixed to the upper portion of the mast is raised or lowered vertically. However, when the working platform is raised to an elevated location, the number of stretchable masts is increased. If the number is increased, this increases the likelihood that the stretched or extended masts may abruptly fall or develop trouble. Furthermore, it was uncertain what mast among the plurality of masts is raised so that it was difficult to raise the mast in turn with precision. Accordingly, it was desired to raise a specific mast alone among the plurality of masts and the masts raised upward in turn are fixed to the other masts by locking means.
In such a lifting mechanism having a plurality of masts for raising the platform, the structure thereof is simple. It is possible to raise the platform on which operators are loaded to a position higher than ladders or step ladders, so that this kind of lifting apparatus has been employed in many cases. However, there has occurred the problem of raising the platform in safety.
Accordingly, it was desired to specify the mast to be raised in turn among the plurality of masts to thereby raise the masts step by step. Furthermore, it was desired to develop a mechanism for connecting the masts with each other with assurance and preventing the platform from falling.